1. Technical Field
This disclosure relates to semiconductor fabrication and more particularly, to the formation of oxides in semiconductor fabrication.
2. Description of the Related Art
Semiconductor memory devices, such as dynamic random access memories (DRAM's) include capacitors accessed by transistors to store data. Deep trench (DT) capacitors are among the types of capacitors used in DRAM technology. Deep trench capacitors are typically buried within a semiconductor substrate.
Processing of semiconductor devices such as DRAM's requires formation and subsequent removal of sacrificial films such as SiO.sub.2 which are called sacrificial oxides (SacOx). These SacOx films may have different uses, such as
1. surface protection, e.g., during implantation, or etch processes (e.g., prior to gate oxide formation); PA1 2. stress relief film (e.g., Pad Oxide); PA1 3. etch stop layer (e.g., Pad Oxide); PA1 4. smoothing of the surface (e.g., SacOx in deep trenches); PA1 5. masking layers (e.g. metal hard mask with subsequent oxidation); PA1 6. structure formation (Poly Pillar formation within deep trenches, DT bottle shape formation); and PA1 7. channeling inhibition during ion implantation. PA1 1. High temperatures, up to 1050 ?C., are required. This significantly contributes to the thermal process budget and may cause stress at device interfaces resulting in dislocations. These dislocations may e.g. cause variable retention time (VRT) problems. PA1 2. The oxide thickness of high temperature SacOx. shows a severe dependence on the Si-crystal orientation resulting in nonuniform structures if polycrystalline surfaces such as trench sidewalls are involved. PA1 3. Thermal SacOx thickness measurement and control are needed. Conventionally the SacOx thickness is measured on the surface of monitor wafers, i.e. an indirect measurement is performed which has to be correlated to the actual structure. If the surface has a different crystal orientation or is polycrystalline (e.g., trench sidewalls), this results in significant deviations between measurement and actual thickness (poor control). PA1 4. Thermal oxides show a high density and are therefore relatively resistant to wet etches. The removal of thermal oxides therefore often results in an undesired attack (degradation) of exposed device surfaces. PA1 5. To obtain homogeneous SacOx thicknesses across wafers, a high temperature uniformity is required resulting in the need for high quality furnaces which are expensive.
The conventional thermal SacOx formation suffers from at least some the following drawbacks:
Therefore, a need exists for a method for forming a sacrificial oxide which does not suffer from the disadvantages of conventional processes. A further need exists for providing a sacrificial oxide process without significant impact to a thermal processing budget.